1. Field of the Invention
The invention relates generally to improvements in windrow elevators for use with asphalt paving machines. More specifically, the invention pertains to an apparatus and a method for re-mixing a continuous stream of segregated asphalt material so it assumes a homogeneous consistency, before it is deposited into the hopper of a paving machine.
2. Description of the Prior Art
The raw material for roadway asphalt, known in the industry as Hot Mix Asphalt (xe2x80x9cHMAxe2x80x9d), is usually prepared at a batch plant, relatively close to the paving site. In addition to the asphalt oil itself, HMA typically includes a mixture of sand, small rocks, and other filler material. For example, shredded rubber tires are sometimes added to the paving mixture, for recycling purposes.
After it is thoroughly mixed at an elevated temperature, the HMA is loaded into the hopper of a xe2x80x9cbelly dumpxe2x80x9d trailer, for transport from the batch plant to the paving site. It is imperative that the HMA is quickly transported to the site, distributed over the roadway, and processed into a smooth mat, before the material cools off. If the HMA cools off too much before the final roadway press is completed, the asphalt coated particles will not form a structurally integrated mat, and premature failure of the asphalt layer will likely result.
At the paving site, the belly dump trailer deposits the HMA in a windrow, extending along the center portion of the roadway. A typical windrow is approximately eighteen inches high, and two to four feet wide. A device known as a windrow elevator progressively collects up the leading edge of the windrow, transports the material upwardly and rearwardly, and then deposits the HMA into the hopper of a trailing paving machine. A paver conveyor in the floor of the paving machine passes the stream of HMA rearwardly, where it comes into contact with a horizontal dam. The dam is vertically spaced from the paver conveyor to level out the layer of HMA thereon. Then, the stream of HMA is discharged off the end of the conveyor, where it is deposited upon the roadway. The still-warm HMA is subsequently compressed by a roller into a firm mat, forming the smooth surface of the roadway.
One of the problems attendant with the manufacture, transport, and distribution of HMA in the process just described is a phenomenon termed xe2x80x9csegregationxe2x80x9d, in the trade. As previously noted, the HMA is composed of different sized materials, ranging from sand granules to small rocks and various fill materials. Owing to the forces of agitation and gravity acting upon these materials during transport and handling, the larger, heavier particles and the smaller, lighter particles tend to separate, and collect in like groups. For example, when the windrow is formed, the smaller particles are concentrated in the central, elevated portion of the windrow and the larger particles are concentrated in the lateral, lower portions of windrow.
When the windrow elevator picks up these size and weight segregated materials, the larger particles and the smaller particles are transported up the elevator in the same relative locations as they existed in the windrow. In other words, across the width of the elevator, the larger particles are concentrated in the lateral regions, and the smaller pieces are concentrated in the middle region. And, when the HMA is deposited onto the paver conveyor, the large and small particles remain segregated from each other in the same fashion. As a consequence, when the HMA mat is formed, there is a concentration of large particles in the lateral portions of the roadway, and a concentration of small particles in the middle of the roadway. This non-homogeneous mixture of HMA across the roadway compromises the strength and integrity of the mat, eventually causing premature fracturing and breakup of the asphalt.
Therefore, the need exists for a device and a method for re-mixing segregated HMA into a uniform mixture, before it is deposited in the hopper of the paving machine.
The need also exists for an HMA re-mixing device which can easily be adapted to an existing windrow elevator, without necessitating major structural or system changes in the windrow elevator.
The need further exists for an HMA re-mixing device which is reliable and effective in moving the concentration of large particles from the lateral portions of the stream of HMA into the median portion of the stream for mixing, to produce a substantially homogeneous mixture of large and small particles in the HMA discharged into the paving machine.
Lastly, the need exists for an HMA re-mixing device which may easily be cleaned after use, without disassembly of components or systems.
The present invention is a re-mixing apparatus strategically mounted at the upper, discharge end of the windrow elevator. The re-mixing apparatus includes an auger assembly mounted for rotation within an auger housing. The auger assembly has first and second helical auger sections, mounted in spaced relation over respective ends of a connecting shaft, leaving an intermediate portion of the shaft therebetween. The auger housing substantially encloses the auger assembly, and in particular the sides, the lower portions, and the outer end portions of both auger sections. The housing also provides an elongated mixing zone, defined by the partially housed volume adjacent and around the intermediate portion of the connecting shaft.
A material inlet is provided at the upper portion of the auger housing to receive a relatively wide stream of material, continuously delivered by the windrow elevator. The material inlet is in communication with the upper portions of the augers and the mixing zone. A material discharge is located in the lower sidewall of the lower portion of the housing, immediately beneath the mixing zone.
At least one hydraulic motor provides rotational drive to a short extension of the connecting shaft, extending through an endwall of the housing. The motor thereby rotates the connecting shaft and the two attached auger sections. The auger sections are of converging, opposite handedness. Thus, when the auger sections are rotated, they are effective to move incoming material delivered from the lateral regions of the windrow elevator, toward the intermediate part of connecting shaft of the auger assembly. The material incoming from the middle region of the windrow elevator is fed directly toward the intermediate portion of the connecting shaft. The material transported inwardly by the auger sections is thereby re-mixed in the mixing zone adjacent and around the connecting shaft, into a homogeneous HMA composition. Then, under force of gravity, the re-mixed HMA material exits downwardly through the material discharge.
The upper portion of the housing is pivotally mounted to the frame of the windrow elevator. A locking mechanism is provided to maintain the housing in a normally closed position, for material re-mixing. To clean the re-mixing apparatus, the locking mechanism is first unlatched. Then, a hydraulic ram, extending between the frame of the windrow elevator and the lower end of the auger housing, is actuated. The force of the ram rotates the housing outwardly, away from the end of the windrow elevator, exposing the inner volume of the housing, including the augers. In this alternate open position, the inner walls of the housing and the augers may be cleaned using a combination of distillate chemicals and mechanical agitation. Withdrawing the hydraulic ram pulls the housing back toward the windrow elevator, placing the housing again into the closed position. Lastly, the locking mechanism is closed to secure the housing in place.
These and other features of the invention will now be described in further detail in the drawings and the detailed description of the preferred embodiment to follow.